Until recently, there were many proposals aimed at improving adhesion of hydrosilation-curable organopolysiloxane compositions, mainly to metal and organic resin substrates, especially to those made from thermoplastic resins. In the past, methods of curing consisted of applying a silane-type primer onto the surface of an adherend, and then curing a hydrosilation-curable organopolysiloxane composition on the primed surface. However, since application of the primer onto the surface was associated with some difficulties, many suggestions were made to provide hydrosilation-curable organopolysiloxane compositions that acquire improved adhesiveness themselves due to introduction of adhesion promoters. Typical examples of such adhesion improvers are the following: an organic silicon compound having in one molecule an epoxy group and a hydrosilyl group (see JP Examined Patent Application Publication [hereinafter referred to as Kokoku] S53-13508); an organic silicon compound having in one molecule an alkoxysilyl group and a hydrosilyl group (see JP Kokoku S53-21026 and JP Kokoku S58-26376); an organic silicon compound having in one molecule a vinyl group and an alkoxy group (see JP Kokoku H6-41563); an organic silicon compound having in one molecule a vinyl group and an epoxy group (see JP Unexamined Patent Application Publication [hereinafter referred to as Kokai] H6-145525); a radical polymer of 3-methacryloxypropyl tris(dimethylhydrogensiloxy) silane, and a radical copolymer of the last-mentioned polymer and a vinyl monomer (e.g., methylmethacrylate or α-methylstyrene) (see JP Kokai H8-291254). Appropriate radical polymers and copolymers that contain hydrosilyl groups are known as adhesion promoters for curable organic resins that are free of alkenyl groups (see JP Kokai 2001-240750).
On the other hand, known in the art is a curable organopolysiloxane composition that consists of an organopolysiloxane with linear-chain alkenyl groups and aryl groups, an organopolysiloxane with branched alkenyl groups and aryl groups, an organohydrogenpolysiloxane with aryl groups, and a hydrosilation reaction catalyst. This curable organopolysiloxane composition is suitable for forming a cured body of high strength that has high light transmittance and can be used in semiconductor devices as a sealing agent (see JP Kokai 2004-143361). Also known are semiconductor devices wherein light-transmitting parts are made from a light-permeable silicone resin (see JP Kokai H7-283441 and JP Kokai 2001-168398).
However, although in the initial stage the self-adhesive hydrosilation-curable organopolysiloxane compositions of the type disclosed in aforementioned JP Kokoku S53-13508 to JP Kokai H6-145525 show excellent adhesion to metals and organic resins, and especially to thermoplastic resins with polar bonds, the adhesion of the adhesive substance to an organic resin, and especially to a thermoplastic resin with polar bonds is deteriorated when the adherend undergoes a wet or dry heat treatment. JP Kokai 2004-14336 does not give any hints to the possibility of adding an adhesion promoter disclosed in JP Kokoku S53-13508 to JP Kokai H6-145525. JP Kokai H8-291254 does not teach that a curable organopolysiloxane can be a material with improved light transmittance properties suitable for use as light-transmitting parts, especially in semiconductor devices. Furthermore, since preparation of the aforementioned radical polymer of 3-methacryloxypropyl tris(dimethylhydrogensiloxy) silane and the radical copolymer of the aforementioned silane and a vinyl monomer (e.g., methylmethacrylate or α-methylstyrene) is carried out without the use of a chain-transfer agent, it is difficult to control the degree of polymerization and to provide recovery of the adhesion promoter that is well compatible with the organopolysiloxane.
JP Kokai 2001-240750 does not teach that radical polymers and radical copolymers with appropriate hydrosilyl groups can be used as adhesion promoters for hydrosilation-curable organopolysiloxane compositions. Neither is it shown that an addition of the aforementioned radical polymers or copolymers to the curable organopolysiloxane composition disclosed in JP Kokai 2004-143361 can improve adhesion during curing of the composition not only to metals, inorganic semiconductors, and ceramics, but also to organic resins, especially to thermoplastic resins having polar bonds. JP Kokai H7-283441 and JP Kokai 2001-168398 only mention light-permeable silicone resins.